GimbalBot twitches to life!

Okay, so we're not quite hovering yet... but I got one of the servo mounts and linkages wrapped up tonight, and I'm satisfied with its functionality. First, the test video:

A few detail pictures:

Cut, drilled, and shaped a 2.4mm thick piece of CFRP as a backing plate for the servo mount:

Drilling the servo bearing mounting holes without a drill press from one side (since everything is glued up already) lead to some hilariously bad servo alignment. In the blurry shot below, you can see how much material I had to file off the left side of the servo mount to get the shaft to turn freely:

A few linkage detail shots. Only thing to note here is the inordinate amount of time I spent hacksawing bolts down to size. Note to self: buy the right length bolts next time. At least they weren't too short:

As I mentioned in the video, the outer servo will have a much harder job; it has to move the whole mess you see above, and I'm guessing I'd overload the servo geartrain without some ramping. Either way, this feels like a good start.

- Zach

Discussions

Michael O'Brien wrote 08/05/2014 at 04:23

Looking goo there man. Be careful with the twitchy movement. I know from your video that you're planning on having acceleration control when pitching the blades when they're moving. Just remember what happens to a gyro when you try to rotate it while spinning. Though the moment of inertia isn't out nearly as far, you'll still have some implied forces you'll have to deal with.

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zakqwy wrote 08/05/2014 at 04:39

Yeah, the rotating mass of the blades (and motor housings) will definitely increase the load on the servo. The increased torque is something one could quantify knowing the motor RPM and inertial mass of the rotating bits, but I haven't done that calculation at this point. My plan is to start with a fairly conservative servo velocity ramping scheme and work from there.

The phrase 'be careful with twitchy movement' actually made me think a bit more about GimbalBot's instrumentation; reducing the magnitude of the shocks transmitted up the frame to the IMU due to fast servo movement will help with accelerometer and gyroscope noise.

Great points, thanks for your input!

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v09 build, part 5

2DOF servo tests

Discussions

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